1. Field of the Invention
The present invention generally relates to a modem system and, more particularly to an adaptive modem modulation system for enabling modems having incompatible modulation methods to communicate with one another.
2. Description of the Prior Art
It is well known that modern telecommunications devices, such as modems, enable transmission of data over communications channels, such as a telephone network, by accessing a network or another modem via a switched data connection through the public switched telephone network (PSTN) or through an Integrated Services Digital Network (ISDN) connection. Modems have the ability to communicate with other modems at a variety of speeds using a number of well-known international standards, generally promulgated by the International Telecommunications Union (ITU). However, in order to connect, the modems must support the same modulation method or mode. Typically, modems connect at data rates selected from a number of maximum data rates, such as 33.6 Kbps, 28.8 Kbps, 14.4 Kbps, 2400 Kbps, 1200 Kbps, 300 Kbps, etc. The modulation mode used in enabling connections at one of the above rates is typically selected from a plurality of ITU standard modulation modes, such as V.34+, V.34, V.32/V.32 bis, V.22/V.22 bis, Bell212 and Bell 103, respectively. Other modulation modes are available as well.
In order to establish a switched data connection, a personal computer (PC) of the originating call includes data communications equipment, such as a modem, that is coupled to the PSTN. Generally, a command is entered into the PC to instruct the modem to dial a telephone number associated with the modem or network the user is attempting to access. After dialing and detecting an answer tone from a far end, or remote, modem of the facility being dialed, both the local modem and the remote modem perform a handshaking procedure to establish the data connection.
In particular, handshaking is performed by the modems each time a data connection is established between the two modems. During the handshaking or initializing procedure, each modem performs a training routine, wherein the modem evaluates the analog communications channel across which the data connection is established. During the training routine, a predetermined training signal is transmitted between the modems from which the modem calculates a set of operating parameters based on an evaluation of the test signal.
Typically, the method employed for selection of a particular modulation mode for transmission of data is the automode method described in U.S. Pat. No. 4,931,250, Greszczuk, which is hereby incorporated by reference. The automode method provides for selection of a common modulation mode negotiated between a call and an answer modem for transmission of data. This is done by automatically choosing the modulation mode to achieve the highest common data rate. Such a method is effective when modems having the same modulation mode are attempting to communicate with one another. For example, two V.34+ standard modems are able to connect and communicate with each other at rates up to 33.6 Kbps because each modem contains the appropriate standard modulation mode specified by the ITU.
However, in many cases, modem manufactures will also include proprietary modulation methods that increase data rates, but that are not approved or specified by the ITU. Such modems may only communicate with other modems having the same proprietary modulation method. Generally, such modulation methods are not compatible with modulation methods of other modem manufacturers that may also be developing their own proprietary modulation modes. Thus, modems that operate using the various proprietary modulation methods are unable to connect using the new modulation methods until a common standard is determined by the ITU.
For example, in 56 Kbps modem technology there exists two competing modulation methods that are incompatible. In particular, X2 modulation developed by U.S. Robotics/3com, and the K56Flex modulation developed by Motorola, are two such competing technologies that are incompatible. Accordingly, the X2 and the K56Flex modems can not communicate with each other at 56 Kbps but may do so at 33.6 Kbps because of the established v.34+ ITU standard. Thus, the higher 56 Kbps speed capabilities of the modem are wasted because of the requirement that the two modems communicate at the slower compatible speed. Because of such incompatibilities between the different modulation methods, many users hesitate and/or delay purchase of cutting-edge technology modems until the ITU specifies a standard at which all modems may intercommunicate at the higher data rate. ITU standardization is a lengthy process, however, and may often take one to two years before agreement on a standard is reached.
The wait-and-see attitude adopted by customers in such cases results in stagnation of market growth as users delay purchase of the product for fear that a modem having one type of new technology will prevent them from connecting to modems having a different type of new technology, thus wasting their investment. In addition, many users are reluctant to purchase a product with enhanced modulation modes when there are few other modems or service providers that will support such a particular enhanced mode to which the user may connect.
Therefore, what is needed is a system for enabling modems having incompatible modulation methods to communicate with each other using the higher data rates made possible by the new, non-standard modulation methods.